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CT Findings of Granulomatous Pneumonitis Secondary to Mycobacterium avium-intracellulare Inhalation: "Hot Tub Lung"

¹ Department of Radiology, Mayo Clinic, 200 First St. SW, Rochester, MN 55905.
² Department of Radiology, Mayo Clinic, Scottsdale, AZ.
³ Department of Laboratory Medicine, Pathology, Mayo Clinic, Scottsdale, AZ.
⁴ Department of Pulmonary & Critical Care Medicine, Mayo Clinic, Rochester, MN

OBJECTIVE. The objective of our study was to describe the CT features of "hot tub lung" caused by exposure to Mycobacterium avium complex (MAC) organisms in contaminated water.

MATERIALS AND METHODS. Chart review was performed to identify all patients with a histologic diagnosis of granulomatous pneumonitis and positive cultures for MAC between January 1, 1995, and July 1, 2004. Individuals identified who also had a hot tub were included in the study. Twelve patients, seven females and five males with an average age of 50 years (range, 13-66 years), who had a CT scan were identified. The CT images were reviewed by two thoracic radiologists who assessed the images for the presence of any parenchymal abnormalities, including nodules, areas of ground-glass attenuation, reticular opacities, and air trapping, on expiratory images. When nodules, reticular opacities, areas of ground-glass attenuation, or a combination of these findings was present, the reviewers visually determined the extent of involvement of the lungs using a scale of < 10%, 10-40%, or > 40%. They also recorded the distribution of the involvement both cephalocaudal and transaxial. Decisions were reached by consensus of the reviewers.

RESULTS. Nodules were present in 10 (83%) of 12 patients. In eight (80%) of 10 patients, the nodules were diffuse with a centrilobular distribution. In the other two, the nodules were randomly distributed with an upper lung predominance. In five patients the nodules showed areas of ground-glass attenuation, whereas in the other five the nodules were solid. Areas of ground-glass attenuation were present in eight (75%) of 12 patients and were bilateral in all cases. The areas of ground-glass attenuation were diffuse in the cephalocaudal plane with a random distribution in the transaxial plane in seven (88%) of eight cases. In the remaining case, the areas of groundglass attenuation had a lower lung predominance with a random distribution in the transaxial plane. Expiratory images showed evidence of air trapping in all seven cases for which these images were available. In one patient, air trapping was the only abnormality identified.

CONCLUSION. The CT findings in patients with hot tub lung include areas of groundglass attenuation, centrilobular nodules, and air trapping on expiratory images. These findings are similar to previously published findings of subacute hypersensitivity pneumonitis. Therefore, in cases in which CT findings suggest hypersensitivity pneumonitis, hot tub lung should also be a diagnostic consideration.

Keywords: CT • granulomatous pneumonitis • highresolution CT • lung disease • Mycobacterium aviumintracellulare

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